How does email open tracking work and what factors can affect its accuracy?

Email open tracking provides insight into how many recipients have opened your email. However, its accuracy can be influenced by several technical factors. Understanding these can help you better interpret your campaign performance.

How Open Tracking Works

We track email opens by embedding a tiny, invisible 1x1 pixel image into each email. When a recipient opens the email and their email client loads the images, this pixel is downloaded from our server. This download is registered as an "open" event (PW_EmailOpen).

Factors Affecting Open Rate Accuracy

Your assumption that this method has limitations is correct. The accuracy of the "Opened" metric can be affected by the following:

• Image Blocking: If a user's email client is set to not download external images by default, the tracking pixel will not load. In this case, an open will not be registered, even if the user read the email. This can lead to an under-reporting of your actual open rate.
• Apple's Mail Privacy Protection (MPP): Apple Mail on iOS, iPadOS, and macOS can pre-load email content, including tracking pixels, through a proxy server. This triggers an "open" event regardless of whether the user actually opened the email, leading to an over-reporting of open rates for these users.
• Email Security Systems: Some corporate or internet service provider (ISP) security systems automatically scan incoming emails for malicious content. This scanning process can involve loading all images, which would trigger the tracking pixel and register a false open before the email even reaches the user's inbox.

Recommended Best Practices for Measuring Engagement

Given the limitations of open-rate tracking, we strongly recommend focusing on metrics that reflect direct user action for a more accurate measure of engagement. These include:

• Click-Through Rate (CTR) / Unique Email Link Clicks: These metrics track when a user actively clicks a link within your email. A click is a clear signal of engagement and interest.
• Custom Events & Conversions: For a deeper understanding of campaign impact, track specific actions users take after clicking through, such as making a purchase, filling out a form, or using a feature in your app.

How to Estimate the Impact of Apple's Mail Privacy

While you cannot filter your email audience by their operating system, you can estimate the number of users leveraging Apple's privacy features. Users who enable Apple's "Hide My Email" feature are assigned addresses with the @privaterelay.appleid.com domain. You can export your subscriber list and search for this domain to get an idea of how many users in your audience may be causing inflated open rates due to MPP.